In an EDS, the space in which the x-ray detector device is placed is required to be maintained as a high vacuum. For this purpose, an adsorbent such as active carbon is cooled by liquid nitrogen. The gas inside the space is adsorbed by the adsorbing action the adsorbent to maintain the degree of vacuum.
In the prior art EDS. as the temperature of the adsorbent rises, the gas adsorbed on the adsorbent released into the space in which the x-ray detector device is installed. Therefore, even when the EDS is not in use, depletion of the liquid nitrogen is not permitted. Consequently, liquid nitrogen must be frequently replenished. In this way, maintenance involves a problem. Furthermore, there is a danger in treating liquid nitrogen.
It is contemplated to use a refrigerator as a means for cooling adsorbent It is expected that the aforementioned problems are solved by this means. However, the space in which the x-ray detector device is placed is normally closed. Therefore, if the operation of the refrigerator is stopped when the EDS is not in use, the temperature of the adsorbent rises. Then, gas which is once adsorbed is released into the space, thus deteriorating the degree of vacuum. Thus, in this system where the adsorbent is cooled by the refrigerator, it is necessary to operate the refrigerator incessantly. In consequence, the components of the refrigerator wear away quickly. As a result, components must be replaced frequently. Also, heat storage materials must be exchanged often.